The present invention relates to surgical implements and, more particularly, to suture anchors for enabling sutures to be attached to bone.
Certain injuries or conditions within the human body often require that bodily tissue be firmly affixed to an adjacent bone structure to secure the tissue in a desired position, for instance, where a ruptured tendon must be reattached to the corresponding bone. To this end, suture anchors have been developed, providing an anchor in the bone to which a suture may be secured, wherein the suture is then used to secure the adjacent bodily tissue. Suture anchors generally are inserted into a bore formed in the bone. There are several types of suture anchors in the prior art, including a barb-type anchor, a corkscrew type anchor, an insert type anchor with offset reorienting suture bore, and a wedge-type anchor. Of these types of suture anchors, the wedge-type anchor has shown good promise.
In practice, wedge-type anchors with attached sutures are first introduced with an insertion tool into a bore drilled into the bone at a location where the bodily tissue must be affixed. The suture anchor generally includes a first gripping portion, such as a sharp edge or a point, and is designed to rotate as it enters the bore or is in the process of being withdrawn therefrom. As the suture anchor rotates, the first gripping portion bites or penetrates the wall of the bore and causes further rotation of the anchor. At the opposite end of the suture anchor, a second gripping portion is typically provided. The second gripping portion penetrates into the wall of the bore generally opposite the first gripping portion as the suture anchor is rotated, thereby wedging the suture anchor within the bore. When the suture anchor has rotated about the first gripping portion as much as the second gripping portion will allow with respect to the bone structure surrounding the bore, the suture anchor is in its seated position where it is anchored in the bore and ready to have adjacent bodily tissue attached thereto.
However, while suture anchors are theoretically designed to work with all bones, the structure of bone can vary greatly depending on the area of the body in which the suture anchor is required. Bones generally include a number of trabeculae disposed throughout. The spacing of the trabeculae within the intermedulary canal of the bone is often a good indicator of the density of the bone. Cortical bone is solid bone without visible interstitial spaces and is typical of the midshafts, or diaphyseal regions, of long bones. Metaphyseal and epiphyseal bone, which is the bone around the joints at the opposing ends of the long bones, has a variable amount of cortical shells with a deeper trabecular structure, wherein the amount of cortical shells may vary greatly. Dense bone typically has small and closely spaced trabeculae, resulting in a hard and strong bone. In comparison, less dense or osteoporotic bone has larger and more widely spaced trabeculae, typically resulting in a softer and generally weaker bone. This less dense bone generally comprises a cancellous bone region about the intermedulary canal. A typical bone structure thus typically includes a cortical layer atop cancerous layer where the proportion of both types of bone may vary. Since the structure of bone may vary significantly from one area of the body to another, the specific performance characteristics required of a suture anchor also vary accordingly. Therefore, suture anchors must be able to function as intended when used in all types of bone structure. Where suture anchors are implanted into dense bone structures, well defined strong gripping edges are required for the suture anchor to securely engage the bore in the bone. However, where the suture anchor is implanted into less dense bone, a large surface area engaging the bone is preferred in order to distribute and reduce the stresses on the relatively weak bone.
Examples of wedge-type suture anchors are found in U.S. Pat. Nos. 5,540,718, 5,626,612, 5,782,863, and 5,879,372 to Bartlett which disclose wedge-type suture anchors based on variants of cone, double cone, and combination cone and cylinder configurations. Additionally, U.S. Pat. No. 5,683,418 to Luscombe et al. assigned to Mitek Surgical Products, Inc., also the assignee of the present invention, discloses wedge-type suture anchors generally varying in shape from triangle to a quadrilateral. Thus, U.S. Pat. Nos. 5,540,718, 5,626,612, 5,782,863, and 5,879,372 to Bartlett and U.S. Pat. No. 5,683,418 to Luscombe et al. are incorporated in their entirety herein by reference.
The Luscombe et al. ""418 patent discloses suture anchors which are angularly shaped, generally approximating a triangle to a quadrilateral and having straight sides. The intersections of major surfaces defining the perimeter of the suture anchor therefore define sharp transitions. Thus, the device disclosed by the ""418 patent is generally more useful in dense bone structures where the sharp gripping edges more effectively bite into the bore in the dense bone. However, with the sharp gripping edges biting into the bone, the ""418 device generally experiences less rotation in both dense and less dense bone than is desirable to properly seat the anchor. Rotation is further inhibited by the long straight surfaces defining the device.
A possible additional limitation of the ""418 device is that the insertion tool used for implanting the suture anchor in the bore is formed from a material having a frangible portion at or near the interface with the anchor which breaks or separates from the anchor after implantation thereof. In the alternative, the ""418 device uses a metallic insertion tool which engages a bore in the anchor in a friction fit. Both insertion tools may experience problems in that the tool with the frangible portion may not provide enough strength for manipulating the anchor within the bore, while the friction fit tool may be difficult to separate from the anchor after implantation thereof.
The Bartlett ""718, ""612, ""863, and ""372 patents disclose wedge-type suture anchors based on variants of cone, double cone, and combination cone and cylinder configurations. These devices use the tip of the cone, or a truncation thereof, to form the edge which first bites into the bone and then provides the point about which the anchor rotates. However, with the reduced cross-sectional area at or near the tip of the cone, this main biting edge may be weaker and prone to breaking in high stress situations, such as where the anchor is being implanted in a dense bone structure. In addition, wedge-type suture anchors generally use a suture, engaged with the anchor through a bore therein, to assist in rotating and seating the anchor within the bone. The wedge-type suture anchors generally have the bore located between the main biting edge and the bore in which the insertion tool is inserted, thereby providing a small moment arm for rotating the suture anchor using the suture. Thus, the suture may be less helpful in assisting the suture anchor to rotate within the bore in the bone, especially in a dense bone structure where the anchor is more difficult to rotate. On the other hand, the Bartlett devices may be more effective in less dense bone where the main biting edge does not experience as high a stress during the seating process for the anchor. Further, the anchor may be able to rotate to a greater extent within the bore in a less dense bone, thus allowing the suture to be more effective in rotating and seating the anchor. Accordingly, since the Bartlett devices are able to rotate more extensively in less dense bone, the anchor can be more effectively seated, thus providing the greater surface area which is desirable for a suture anchor used in less dense bone.
Thus, there exists a need for a suture anchor which will effectively anchor a suture within a bore in a bone while also preferably functioning equally in bones of differing densities, from hard dense bone to softer, less dense bone.
The above and other needs are met by embodiments of the present invention which provide a suture anchor particularly adapted for effectively anchoring sutures in all types of bone structures from hard dense cortical bone to softer, less dense cancellous bone. In one embodiment, the suture anchor comprises a body having a bore-abutting surface with a leading gripping edge at one end of the bore-abutting surface, a trailing gripping edge at the other end thereof, and a closing surface engaging the leading and trailing gripping edges generally opposite the bore-abutting surface. The body further defines a suture bore extending transversely therethrough and an inserter bore adapted to receive an insertion tool. A suture engages the suture anchor through the bore such that it is adapted to engage bodily tissue to be secured to the bone.
The suture anchor is preferably quadrilaterally shaped with the side having the longest dimension comprising the bore-abutting surface. A leading surface intersects one end of the bore-abutting surface at an acute angle to form the leading gripping edge. A trailing surface intersects the other end of the bore-abutting surface at an acute angle to form the trailing gripping edge. The configurations of both the leading and trailing gripping edges may be varied according to the structure of the bone in which the anchor is to be inserted. A closing surface having an arcuate portion and a substantially linear portion engages the ends of the leading and trailing surfaces, respectively, opposite the bore-abutting surface, to form a generally quadrilaterally shaped body. The body further defines a suture bore extending transversely therethrough and disposed adjacent the trailing gripping edge, wherein the suture bore may vary in size. The suture bore also engages a suture, wherein the suture passes through the suture bore and is adapted to engage bodily tissue adjacent the bore. In addition, in order to facilitate insertion of the suture anchor within the bore in the bone, the body defines an inserter bore adapted to receive an insertion tool. The inserter bore preferably extends through the leading surface such that it is angularly disposed with respect to the bore-abutting surface. More preferably, the inserter bore is disposed between the leading gripping edge and the suture bore and has a uniform cross-sectional shape along its length. The inserter bore preferably has a non-circular cross-section, where a generally square shape is most preferred.
The suture anchor may also be varied in size and configuration according to characteristics and structure of the bone in the affected area of the body and the performance characteristics required of the suture anchor. Preferably, the body of the suture anchor is comprised of a biocompatible material, with a bioabsorbable material being particularly desirable. The body may be comprised of, for instance, polylactic acid, polydioxanone, polyglycolic acid, or the like, with polylactic acid being most preferred.
A further advantageous aspect of the present invention comprises an alternate embodiment of a suture anchor configured to permit knotless sutures to be used to secure bodily tissue to the adjacent bone structure. The alternate knotless embodiment of the present invention comprises generally the same suture anchor configuration as the embodiments previously described, but further including a notch in the bore-abutting surface and a suture forming a loop through the suture bore. Preferably, the suture is adapted to engage the bodily tissue to be secured to the bone. Once the bodily tissue is engaged, the suture wraps back about the body and engages the notch. The body is then implanted into the bore in the bone to secure the bodily tissue thereto without requiring further knotting of the suture.
Still another advantageous aspect of the present invention comprises an insertion tool for inserting a suture anchor within a bore in a bone. The insertion tool generally comprises a rigid shaft having opposed ends with a tip engaged with one end of the shaft. The tip further has a proximal end operably engaged with the shaft and a distal end adapted to be engaged with an inserter bore in a suture anchor. The tip is preferably comprised of a shape memory material, such as a nickel-titanium alloy, with a non-circular cross-section corresponding to the cross-sectional shape of the inserter bore in the body. In addition, it is further advantageous for the tip to have a uniform cross-sectional shape along its length to facilitate ease of separation from the inserter bore. Further, a non-circular or, more particularly, a generally square shape of the tip minimizes rotation of the suture anchor about the axis of the tip. Thus, the use of a shape memory material for the tip, and a shape for the tip which inhibits rotation of the anchor with respect thereto, allows the tip to be small in size. The small size of the tip thereby allows the tool and the suture anchor to be more easily manipulated within the bore and allows for small-sized suture anchors.
Yet a further advantageous aspect of the present invention comprises a kit for anchoring a suture in a bore in a bone. According to one embodiment, the kit comprises at least one insertion tool and at least one suture anchor according to the previously described embodiments thereof. At least one boring bit may also be included, with the bit capable of forming a bore of sufficient size in a bone to accommodate a provided suture anchor.
Another advantageous aspect of the present invention comprises a method of implanting a suture anchor within a bore in a bone. A suture anchor is first urged into engagement with the bore using an insertion tool angled with respect to the bore such that a bore-abutting surface of the suture anchor is engaged with the wall of the bore. The insertion tool is then elastically deformed to urge the suture anchor into the bore such that the bore-abutting surface remains engaged with the wall of the bore as the suture anchor is inserted. The suture anchor is then manipulated within the bore by moving the insertion tool to the diametrically opposite side of the bore such that the suture anchor rotates about a leading gripping edge thereof. After the insertion tool is removed from the suture anchor, the suture anchor is further rotated into a seated position within the bore by the exertion of a tensile force on the suture passing through the suture bore. The suture anchor thus further rotates about the leading gripping edge, for example, up to about 90 degrees from its insertion angle, such that both the leading gripping edge and a trailing gripping edge are engaged with the wall of the bore. The suture anchor attains a seated position when the engagement of the trailing gripping edge with the wall of the bore prevents further rotation of the suture anchor.
Therefore, according to embodiments of the present invention, the leading gripping edge formed by the intersection of two surfaces provides a more robust structure than the tip of a cone, thereby providing a stronger suture anchor for high stress situations such as implantation of the anchor in high density bone. Further, the arcuate transition between the leading and trailing gripping edges facilitates rotation of the suture anchor in a bore in various bone structures, from dense cortical structures to less dense cancellous structures, thereby improving the seating ability of the suture anchor and requiring less effort to achieve the necessary rotation. In addition, the trailing gripping edge formed by the intersection of two surfaces provides a sharp gripping edge which is desirable in a dense bone structure. However, when included with the closing surface having an arcuate portion, the sharp trailing gripping edge permits the suture anchor to engage the bore in a less dense bone structure after the anchor has been rotated to provide the high seating surface area which is desirable for a less dense bone structure. Thus, the suture anchor according to embodiments of the present invention provides a mechanism for effectively anchoring a suture within a bore in a bone while also functioning equally in bones of differing densities, from hard dense bone to softer, less dense bone. Further, the uniform non-circular configuration of the inserter bore/insertion tool interface minimizes rotation of the suture anchor about the axis of the tip while facilitating a robust and easily connectable/disconnectable interface between the insertion tool and the suture anchor.